The current PBX (Private Branch Exchange) services in hotels are minimally used by customers due to:                Expensive call rates.        Clients use their mobile phone (cheaper and more convenient).        
For business customers, price is not so important but ease of use and convenience is the most important feature.
For personal users, price becomes much more important although convenience still plays a key role.
The proposed solution addresses the two points highlighted above and supports a commercial proposition that generates more revenue for the hotels while it offers more services to the hotel clients at a cheaper price.
Current PBX are based on fixed technology and there is a fixed telephone at every hotel room. Call rates could be lowered, but convenience cannot be improved. The user must be in the room to receive/make calls.
PBX solutions that support mobile handsets are available in the market and a VPN can be created between the mobiles of multiple users. However, the current solutions require a real mobile phone number (MSISDN) assigned to every terminal/extension. This means an overhead for the hotel.
The present invention solves those problems by making use of a mobile PBX, so that every hotel will have its own VPN numbers that can be used as room extensions.
It is well-known that abbreviations and acronyms are frequently used in the mobile telephony field. Below is a glossary of acronyms/terms used throughout the present specification:    DTMF Dual Tone Multi-Frequency    HLR Home Location Register    IMS IP Multimedia Subsystem    IMSI International Mobile Subscriber Identity    IN Intelligent Network    IVR Interactive Voice Response    MNO Mobile Network Operator    MO Mobile Originated    MS Mobile Station    MSC Mobile Switching Centre    MSISDN Mobile Station International Subscriber Directory Number    MSS MSC Server    MT Mobile Terminated    PBX Private Branch Exchange    SCP Service Control Point    SDP Service Data Point    SMS Short Message Service    VPN Virtual Private Network